Fuel-injection pump for turbocharged diesel engine

Abstract: A fuel-injection pump for a turbocharged diesel engine not equipped with a boost compensator is able to suppress the generation of black smoke when the engine is subjected to sudden acceleration from a low-speed state, or to low speed, high load operation, by reducing the fuel injection quantity. The pump comprises a plunger barrel (24) in which are formed intake and exhaust ports (32,33) that communicate with a fuel reserve chamber (30), said intake and exhaust ports (32,33) being constituted by a large diameter main port (32) and a small diameter sub-port (33) arranged so that the upper edge of the sub-port (33) is not above the upper edge of main port (32), a plunger (25) disposed within the plunger barrel (24), an inclined lead (35) being formed on the plunger (25) at a position that permits communication with the intake and exhaust ports (32,33), an upper sub-lead (36) being formed on the head portion of the plunger (25) that is able to communicate with the sub-port (33) over a prescribed range of rotation by the plunger (25), and which permits the sup-port (33) to communicate with the upper sub-lead (36) even when the main port (32) is closed by the upper edge of the plunger (25).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a fuel injection pump for a diesel engine as known from US-A-2 361 817. It is preferably fitted with a turbo-charger, and more particularly it refers to a fuel-injection pump for a turbocharged diesel engine that has an injection compensation mechanism. Description of the Prior Art In a turbocharged diesel engine, exhaust gas from the combustion chamber (engine cylinder) is used to compress intake air which is then supplied to the engine to increase the power of the engine. In a conventional turbocharged diesel engine, changes in the boost pressure provided by the turbocharger is a function of the fuel injection pump speed in rpm (N) and injection quantity or load (Q). A conventional turbocharged diesel engine will now be described briefly, with reference to Figure 7. In Figure 7, a turbocharged diesel engine 1 has a engine body 2, a piston 3, a turbocharger 4, a governor 5 and a fuel injection pump 6. A crankshaft 8 is turned by the reciprocating movement of the piston 3 in a combustion chamber 7. The turbocharger 4 uses the exhaust gas from an exhaust manifold 9 to compress intake air, and the air thus compressed is delivered to the combustion chamber 7 via an intake manifold 10. The governor 5 controls the fuel injection quantity in accordance with the speed (rpm) of the turbocharged diesel engine 1. The fuel injection pump 6 has a camshaft 11 driven by the crankshaft 8, an injection pipe 12, and an injection nozzle 13 arranged in opposition to the combustion chamber 7. One method that is commonly used to evaluate the performance of an engine such as the turbocharged diesel engine 1 consists of measuring the level of black smoke that is generated when the engine is subjected to sudden acceleration from a low idle. However, a problem with the diesel engine 1 is that sharply accelerating the engine from a low idle causes an excessive quantity of fuel to be injected and black smoke to be produced. This is explained below. The graph of Figure 8 shows the relationship between pump speed N (or engine speed) and injection quantity Q. In the graph, the relationship in the case of an engine that does not have a turbocharger 4 is indicated by a broken line, while the higher injection quantity Q of the engine 1 equipped with the turbocharger 4 is indicated by a solid line. Injecting more than the proper quantity of fuel during low-speed operation causes black smoke to be produced. In a conventional arrangement, a device known as a boost compensator (not shown) was used to control the relationship between turbocharger 4 boost pressure, and pump speed N and injection quantity Q. Specifically, with reference to Figure 9, the boost compensator suppresses the emission of black smoke during low-speed operation by reducing injection quantity Q (refer to the "Zone of injection quantity control by boost compensator" in Figure 9). That is, when the boost pressure provided by the turbocharger 4 is low, the boost compensator limits the generation of black smoke to a certain level by setting the control rack position R further in. However, in the case of turbocharged diesel engines not equipped with a boost compensator, particularly turbocharged diesel engines used for industrial applications, the injection quantity Q becomes excessive and all turns into black smoke, creating a major problem with respect to engine evaluation. Furthermore, most turbocharged diesel engines 1 are small units. In order to newly equip such engines with a boost compensator, it is necessary to alter the linkage (not shown) used for the governor 5. Also, in the case of turbocharged diesel engines in which the governor 5 is not directly connected to the fuel injection pump 6 but is provided on the engine side, the limited space also makes it difficult to fit a boost compensator. This has produced a demand for a means of solving the problem of black smoke generated during sudden acceleration from a low idle condition in turbocharged diesel engines that do not have a boost compensator and cannot readily be fitted with such a boost compensator. SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel-injection pump for a turbocharged diesel engine that is not equipped with a boost compensator, and which by reducing the fuel injection quantity is able to suppress the generation of black smoke when the engine is subjected to sudden acceleration from a low-speed state, or to low speed, high load operation. In accordance with the present invention, the above object is attained by, instead of the described boost compensator, a fuel-injection pump according to claim 1. Thus, the fuel-injection pump for a turbocharged diesel engine has a plunger barrel in which are formed a large diameter main port and a small diameter sub-port, and a plunger in which is formed an upper sub-lead able to communicate with the sub-port. By employing a plunger barrel with a main port and a sub-port and a plunger with an upper sub-lead, utilizing the fuel throttling effect of the upper sub-port at high engine speeds and, with the control rack set at the same position, reducing the fuel injection quantity at low speeds, the fuel-injection pump according to this invention can provide the same functionality as a boost compensator, and therefore can improve engine performance without any changes to the principle parts of conventional diesel engines or fuel injection pumps. Moreover, while in the case of a boost compensator, reducing the fuel injection quantity at low speeds is effected mechanically by controlling the position of the control rack, with the pump of this invention, the injection quantity characteristics can be adjusted based on the difference between the static effective stroke (low speed) and dynamic effective stroke (high speed) with a fixed control rack position. Further features of the invention, its nature and various advantages will become more apparent from the accompanying drawings and following detailed description of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a vertical cross-sectional view of an embodiment of the fuel-injection pump for a turbocharged diesel engine according to this invention; Figure 2 is a vertical cross-sectional view of the main parts of portion II of Figure 1; Figure 3 shows details of the leads at the top part of the plunger; Figure 4 is a vertical cross-sectional view to illustrating the operation of the pump during low-speed operation; Figure 5 is a vertical cross-sectional view illustrating the operation of the pump during high-speed operation; Figure 6 is a graph of the N-Q characteristics of the pump provided with a preflow effect plunger; Figure 7 shows the arrangement of a conventional turbocharged diesel engine; Figure 8 is a graph showing the relationship between pump (or engine) rotational speed N and fuel injection quantity Q; and Figure 9 is a graph showing the relationship between pump (or engine) rotational speed N and fuel injection quantity Q when a boost compensator is used to suppress the generation of black smoke at low rotational speed by reducing injection quantity Q. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a fuel injection pump 20 according to this invention will now be described with reference to Figures 1 to 6. Parts that are the same as in Figure 7 have been given the same reference symbols, and further details thereof are omitted. Figure 1 is a cross-sectional view of the fuel-injection pump 20 for a turbocharged diesel engine, and Figure 2 is a cross-sectional view of the main parts of portion II of Figure 1. The fuel injection pump 20 has a pump housing 21, a cam 22 affixed to a camshaft 11 (Figure 7), an injection quantity control rack 23, a plunger barrel 24, a plunger 25, a delivery valve 26 and a delivery valve holder 27. The cam 22 is driven via the camshaft 11 by a crankshaft 8 of a diesel engine 1, thereby causing the plunger 25 to be reciprocated vertically via tappet roller 28. The control rack 23 is linked to the accelerator (not shown) via governor 5 (Figure 7). Moving the control rack 23 in a direction normal to the drawing sheet via control sleeve 29 rotates the plunger 25 axially through a prescribed angle. The plunger barrel 24 is fixed within the pump housing 21 to which it is attached. The plunger 25 is accommodated inside the plunger barrel 24 so that the plunger 25 can reciprocate and rotate therein. A fuel reserve chamber 30 is defined by the plunger 25 and the pump housing 21, and the space between the plunger barrel 24 and the delivery valve 26 forms a fuel pressure chamber 31. As shown enlarged in Figure 2, formed in the plunger barrel 24 are a main port 32 and a sub-port 33 through which fuel is drawn in and expelled. The upper edge 32A of the main port 32 and the upper edge 33A of the sub-port 33 are formed at the same height or horizontally at the same position and separated in the circumferential direction by 180 degrees. The main port 32 and sub-port 33 may also be formed so that the upper edge 33A is lower than the upper edge 32A. Fuel from the fuel reserve chamber 30 is sucked in by the reciprocation of the plunger 25 in the plunger barrel 24 and compressed in the fuel pressure chamber 31. When the delivery valve 26 opens, the fuel is delivered under pressure via injection pipe 12 (Figure 7) to the injection nozzle 13. Figure 3 is a diagram of the leads at the top part of the plunger 25, showing the mutual positional relationship between the main port 32 and sub-port 33. Formed in the top part of the plunger 25 are a vertical fuel passage 34 that communicates with the pressure chamber 31, an inclined lead 35 that communicates with the vertical fuel passage 34, and an upper sub-lead 36 that communicates with the pressure chamber 31. As shown in the drawing, the upper sub-lead 36 can oppose the sub-port 33 from normal load to startup, and the main port 32 can oppose the upper edge 25A of the plunger 25. Here, normal load encompasses a range of operation extending from low speed operation such as idling, to high speed operation and high idling (reduction of fuel injection quantity by the governor 5 when high speed, high load rated rotational speed zone is exceeded), under high loads and low loads other than at startup. With respect to Figure 3, as the plunger 25 is vertically reciprocated within the plunger barrel 24 by the action of the cam 22, the upper sub-lead 36, vertical fuel passage 34 and inclined lead 35 are shifted vertically relative to the fixed-position main port 32 and sub-port 33. Also, the rotation of the plunger 25 in the plunger barrel 24 by the action of the control rack 23 shifts the upper sub-lead 36, vertical fuel passage 34 and inclined lead 35 horizontally relative to the main port 32 and sub-port 33. In the fuel injection pump 20 thus configured, when the plunger 25 descends, fuel in the fuel reserve chamber 30 is sucked into the pressure chamber 31 via the main port 32 and sub-port 33. When the plunger 25 ascends, fuel compression begins from the point at which the main port 32 and sub-port 33 are closed by the upper edge 25A of the plunger 25 and the upper edge 36A of the upper sub-lead 36, and delivery of the fuel stops when the main port 32 aligns with the inclined lead 35. That is, the stroke of the plunger 25 from bottom dead center to the start of fuel delivery is a prestroke. The depth or height of the upper sub-lead 36 is preflow stroke L1. The stroke from the closing of the sub-port 33 to the opening of the main port 32 is static (low speed operation) effective prestroke L2, and the stroke from the closing to the opening of main port 32 is dynamic (high speed operation) effective stroke L3. When the engine is under normal load operation, the main port 32 is opposite the upper edge 25A of the plunger 25 and the sub-port 33 is opposite the upper sub-lead 36. At idling and other low speed operation, the position of the main port 32 is further to the left relative to the inclined lead 35 shown in Figure 3, reducing the effective stroke, and as shown in Figure 4, the sub-port 33 is in alignment with the upper sub-lead 36, so the delivery of fuel substantially starts when the sub-port 33 is closed by the upper edge 36A of the upper sub-lead 36. When the rotational speed is increased during high speed operation the main port 32 is shifted to the right of the inclined lead 35, increasing the effective stroke, and as shown in Figure 5, as the throttling effect of the sub-port 33 causes fuel delivery to start before the sub-port 33 is completely closed by the upper edge 36A of the upper sub-lead 36 (the prestroke effect), fuel injection timing is advanced. Figure 6 is a graph of the N-Q characteristics of the pump 20 with this preflow effect plunger 25. With the preflow effect plunger 25, the above function results in the N-Q characteristics indicated in Figure 6 by the solid lines rising to the right (with the control rack 23 at the same position, injection quantity increases at the high speed side). The broken lines indicate the results obtained with a conventional plunger not having an upper sub-lead 36. Thus, the fuel injection pump 20 has a fuel injection quantity suppressing effect that is the equivalent of the injection quantity suppressing effect provided by a boost compensator, as indicated by the "Zone of injection quantity control by boost compensator" in Figure 9. Especially when rotational speed is increased by sudden acceleration from a low idle, the fuel injection pump 20 can prevent the generation of black smoke caused by an excessive quantity of fuel injection by holding the fuel injection quantity to the appropriate level. Moreover, there is the advantage that simply by replacing the plunger and plunger barrel, a conventional fuel injection pump can be given this black smoke generation prevention effect without altering the basic pump arrangement. In accordance with the invention described above, a plunger having an upper sub-lead for a sub-port is used instead of a boost compensator. The plunger be used in place of a standard plunger, whereby it enables the generation of black smoke to be kept to a low level without any external change to the fuel injection pump or diesel engine. Thus, the boost compensator can be omitted and the governor linkage therefore simplified.

Claims: A fuel injection pump for a turbocharged diesel engine, said engine having a turbocharger, a piston driven by combustion in a combustion chamber of intake air supercharged by the turbocharger, a crankshaft rotated by the driving of the piston, a governor able to control a fuel injection quantity in accordance with a differential between a rotational speed of the crankshaft and a set target rotational speed, said fuel injection pump comprising: a pump housing, a cam (22) driven by rotation of the crankshaft (11), a plunger barrel (24) that is affixed to the pump housing and in which are formed intake and exhaust ports that communicate with a fuel reserve chamber, said intake and exhaust ports being constituted by a large diameter main port (32) and a small diameter sub-port (33) arranged so that the upper edge (33A) of the sub-port is below or at the same height as the upper edge (32A) of the main port, a plunger (25) disposed within the plunger barrel that can be moved reciprocally by the cam and rotated by a control rack operated in conjunction with the governor, an inclined lead (35) formed on the plunger at a position that permits communication with the intake and exhaust ports, an upper sub-lead (36) formed as a recess on the head portion of the plunger (25) that is able to communicate with the sub-port (33) over a prescribed range of rotation by the plunger, and which permits the sub-port (33) to communicate with the upper sub-lead (36) even when the main port (32) is closed by an upper edge of the plunger, and a fuel pressure chamber formed between the plunger and the plunger barrel into which fuel is sucked in from the fuel reserve chamber and delivered under pressure by the reciprocating movement of the plunger, characterized in that said ports and sub-lead are arranged in such a way that in a high load position of the plunger (25) the main port (32) is opened and closed by the upper edge (25A) of the plunger and the sub-port (33) is opened and closed by the upper sub-lead (36). A fuel injection pump according to claim 1, wherein there is provided no boost compensator in which, when the boost pressure produced by the turbocharger is low the fuel injection quantity is limited by inserting the control rack further in. A fuel injection pump according to claim 1, wherein the main port is able to communicate with the inclined lead over a prescribed range of rotation by the plunger.

Inventors: KATO HIROAKI, TANAKA NORITOSHI, YASHIRO HIDEKATSU, KATO, HIROAKI, TANAKA, NORITOSHI, YASHIRO, HIDEKATSU, KATO, HIROAKI, C/O ZEXEL CORP., TANAKA, NORITOSHI, C/O ZEXEL CORP., YASHIRO, HIDEKATSU, C/O ZEXEL CORP.
Applicants: ZEXEL CORP, ZEXEL CORPORATION
Application year: 1994
Main classification: F02M59
IPC codes: F02M59, F02B3